1. Field of the Invention
The present invention relates to an apparatus for controlling behavior of a vehicle, which is used for restraining the vehicle behavior such as a drift-out or spin.
2. Prior Art
For example, as described in the Japanese Laid-open Patent Publication No. 6-183288 or No. 7-223520, there is conventionally well known an apparatus which detects an unstable state of the vehicle such as the above-mentioned drift-out (under-steering state) or spin (over-steering state) so as to restrain it. In the apparatus, the behavior of the vehicle is controlled in accordance with the deviation between the control target yaw rate and the actual yaw rate.
In the above-mentioned conventional apparatus for controlling the behavior of the vehicle, however, the start and completion of the control is determined in accordance with whether the deviation between the control target yaw rate and the actual yaw rate is larger than a threshold or not. Thus it is probable that the control is completed nevertheless the behavior of the vehicle has not become stable yet. Particularly, in such a case that the driver avoids an obstruction or the like, it is probable that it is required to execute the behavior control continuously after the behavior control has been executed once. In this case, the start and completion of the behavior control may be repeated. In consequence, for example, it may be feared that a behavior change is caused due to the completion of the behavior control, or the driving operation becomes unstably.
The present invention has been achieved in view of the above-mentioned circumstances, and has an object to provide an apparatus which can adequately complete the behavior control.
The present inventors have performed the present invention to achieve the above-mentioned object, in consideration of such a matter that the completion of the behavior control is determined in accordance with the driver""s operation of the steering wheel or the state of the vehicle.
In concrete, an apparatus for controlling behavior of a vehicle according to the present invention includes a controller for estimating behavior of a yaw rate of the vehicle using of a first target yaw rate calculated on the basis of a steering angle, a second target yaw rate calculated on the basis of lateral acceleration of the vehicle and an actual yaw rate caused in the vehicle, while controlling braking force for the vehicle to control the behavior of the yaw rate on the basis of estimated results. Further, the controller completes (terminates) controlling the behavior of the vehicle if a completion condition established on the basis of an operation of a driver or a state of the vehicle is achieved during over-steering control of the vehicle. An example of the completion condition is such that a steering wheel of the vehicle is operated so as to increase the steering angle in a direction of the actual yaw rate. Hereupon, the term xe2x80x9cover-steering controlxe2x80x9d means control for restraining the over-steering state of the vehicle.
In this case, the steering wheel is operated to increase the steering angle, although the driver usually operates the steering wheel in the counter direction (that is, direction to decrease the steering angle, or turning back direction) when the vehicle is under the over-steering state. In consequence, it may be considered that the above-mentioned operation of the steering wheel is performed, for example, to corner by intentionally making the vehicle spin. In the above-mentioned case, the behavior control, namely the control for avoiding the over-steering state, interferes with the driver""s operation. Therefore, in the present invention, the interference between the behavior control and the driver""s operation is to be prevented by completing the behavior control rapidly.
The completion condition is not limited to the above-mentioned one, but other conditions may be used. For example, the behavior control may be completed when the vehicle is running straight in a stable state during the over-steering control. Hereupon, the judgement whether the vehicle is running straight may be performed, for example, by judging whether the steering angle is stable at an approximately neutral position.
In this case, it may be considered that the driver calmly operates the steering wheel because the vehicle is running straight in the stable state. If the control for avoiding the over-steering state is executed by controlling the braking force in the above-mentioned case, it is feared that the control may interfere with the driver""s operation. Therefore the behavior control is completed so as to entrust the driver""s operation with the avoidance of the over-steering state.
Each of the above-mentioned two completion conditions is based on the driver""s operation of the steering wheel. However, there is such a case that the behavior control may be completed in view of the state of the vehicle although the driver is not performing any particular operations.
For example, the behavior control may be completed when a deviation between the second target yaw rate calculated on the basis of the lateral acceleration and the actual yaw rate caused in the vehicle is stable in a region lower than or equal to a preset value. In this case, it may be considered that it is not necessary to execute the behavior control because the deviation between the second target yaw rate and the actual yaw rate is small. In addition, because the state of the control is stable, it may be considered that the state of the vehicle is also stable so that the behavior control is completed.
Meanwhile, for example, the behavior control may be completed when an estimative brake fluid pressure estimated on the basis of a braking degree (quantity) generated by executing the behavior control is approximately identical to a fluid pressure of a master cylinder during the over-steering control. In this case, it may be considered that the reason why the estimative brake fluid pressure is approximately identical to the fluid pressure of the master cylinder is because it is under such a state that behavior control has been completed, such as the state that the braking force is not substantially controlled. Therefore the behavior control is completed.
Further, the above-mentioned completion condition may be made stricter as follows. That is, for example, the behavior control may be completed when the estimative brake fluid pressure is approximately identical to the fluid pressure of the master cylinder, and a slip angle becomes small. In this case, it may be considered that the behavior control has been substantially completed. Further, it may be considered that the vehicle does not cause a lateral slip, because the slip angle is small. Therefore the behavior control is completed.
Meanwhile, for example, the behavior control may be completed when the estimative brake fluid pressure is approximately identical to the fluid pressure of the master cylinder, and all of the absolute values of the first and second target yaw rates and the absolute value of the actual yaw rate become smaller than a preset value. In this case, because all of the absolute values of the first and second target yaw rates and the absolute value of the actual yaw rate are smaller than the preset value, it may be considered that the vehicle is running approximately straight while the steering wheel is not operated, so that it is not necessary to execute the behavior control. In addition, because the estimative brake fluid pressure is approximately identical to the fluid pressure of the master cylinder, it may be considered that the control of the braking force is not also executed. Therefore the behavior control is completed.
Moreover, for example, the controller may complete the behavior control when the slip angle is small, and among the first and second target yaw rates and the actual yaw rate, the absolute values of any two ones are smaller than a preset value while the absolute value of the remaining one is resemble to the preset value. In this case, the completion condition is looser than that of the above-mentioned case. In this state, however, it may be considered that the vehicle is running with sufficient grip force while the behavior of the vehicle is following the steering angle. Therefore the behavior control is completed.
By the way, in some cases of the above-mentioned various cases, it may be considered that the completion condition is accidentally achieved, nevertheless the behavior control should be further continued. Therefore the controller may delay completing the behavior control till the state meeting the completion condition is continued for a preset time. That is, the behavior control may be completed after the preset time has passed from the time point that the completion condition was achieved. In other words, the behavior control may be completed if the state meeting the completion condition is continued for the preset time.
As described above, by completing the behavior control on the basis of the state of the vehicle also, not only on the basis of the deviation between the control target yaw rate and the actual yaw rate, it may be prevented that the start and completion of the behavior control are repeated.